Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method involves floating a transducer head in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by airflow generated between the sliding surfaces of the transducer head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the transducer head can be freely moved in both the circumferential and radial directions allowing data to be recorded on and retrieved from the surface of the disk at a desired position. It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height or glide of the transducer head.
There are, however, inevitable topographical asperities, typically of only a few microns in diameter and few microinches in height, formed on the surface of a conventional magnetic recording media, which surface comprises a data zone and a landing zone. These asperities stem from a variety of sources, e.g., thermal treatment, magnetic orientation of the magnetic alloy layer, groove generation and polishing. Moreover, these asperities vary in height, diameter and frequency among magnetic recording media.
Conventional disk drives are manufactured with precise specifications, including a precise maximum glide height for a transducer head flying above the data zone. In recognition of the inevitable topographical asperities formed on the data zones of magnetic recording media, conventional practices comprise testing each magnetic recording medium to determine if the particular magnetic recording medium satisfies the maximum glide height requirement for a particular magnetic disk drive. Such testing typically comprises the use of a device known as a glide tester commercially available from various sources, such as Cambrian or Phase-Matrix of California.
Conventional glide testers accommodate the particular magnetic recording medium to be tested and a reference disk typically containing a single protrusion thereon formed by photolithographic techniques and having a defined height, i.e., glide height. The reference disk is rotated and a transducer head lowered until the transducer head contacts the protrusion at which point a first electrical signal is generated indicative of glide height as a function of the height of the reference disk protrusion. The magnetic recording medium is then rotated and the transducer head lowered onto the media surface until contact is made to generate a second electrical signal. The second electrical signal is compared to the first electrical signal to determine whether the tested magnetic recording medium satisfies the glide height requirement for a particular disk drive. The proper functioning of the glide tester, manifestly, requires the generation of a strong, stable and repeatable signal for effective comparison. Of particular significance is the necessity for the protrusion on the reference disk to accurately simulate topographical asperities inevitably present on the surface of a magnetic recording media.
There are significant disadvantages attendant upon conventional practices for manufacturing and employing a reference disk comprising a single protrusion formed by photolithographic techniques. For example, the protrusion formed by photolithographic techniques is significantly greater in diameter than actual topographical asperities formed on the data zone of a magnetic recording medium and, hence, does not provide a basis for an accurate simulation. The protrusion typically produced by a photolithographic technique, such as made by StorMedia or Akashic of California, is about 100 .mu.m to about 200 .mu.m in diameter; whereas, topographical asperities are generally only a few microns in diameter. A single protrusion formed by a photolithographic technique does not accurately simulate the aerodynamic conditions generated by a plurality of protrusions characteristic of inevitable topographical asperities. Additionally, a single photolithographically formed protrusion wears out in a short period of time as a result of repeated contacts with the transducer head of the glide tester and, hence, yields inconsistent results. Moreover, the reference disk comprising a single photolithographically formed protrusion must be replaced frequently. It is also extremely expensive to produce a reference disk having a protrusion formed by photolithographic techniques.
Accordingly, there exists a need for a reference disk for use in a glide tester to accurately determine the glide height above the surface of a magnetic recording medium. There also exists a need for an efficient and cost effective method to produce a reference disk containing protrusions simulating actual topographical asperities on the surface of a magnetic recording media.